Various types of transistors are used in control systems. For example, Metal Oxide Semi-conductor Field Effect (MOSFET) transistors are used in many control systems. In one example, a microprocessor may create the control signal and that control signal is used to control the MOSFET transistor.
Different operating parameters define the performance of MOSFET transistors. One of these parameters is the “slew rate” of the control signals that are used to control the MOSFET. The slew rate refers to the maximum voltage change allowed per unit time. If the slew rate is not controlled, negative effects can occur with respect to system operation. The higher the slew rate, the faster the signal transitions from one value to another.
MOSFETs can be used to control pulse width modulation (PWM) processes where the pulse width changes (is modulated) based upon input provided by the MOSFET. However, if the slew rate of the signal created by the MOSFET varies (due to a variety of factors such as MOSFET component variation, layout variation, temperature variation, and battery voltage) the PWM function will be inaccurate and a system might not perform in a satisfactory manner.
Present control approaches preset the slew rate to some preset value. Unfortunately, this means that variations of slew rate cannot be accounted for by the system. This has led to sub-optimal performance in some systems and some user dissatisfaction with previous approaches.
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